Achieving future fuel efficiency improvements in medium and heavy duty commercial trucks and buses will be a challenging task for commercial truck and diesel engine manufacturers. Over the past several decades, fuel efficiency improvements have been realized largely through the application of computer technology to the design and development of engines and powertrains and through the adoption of sophisticated engine control systems in commercial trucks. Hybrid powertrains have contributed to fuel economy improvements, but at significantly increased manufacturing costs that raise prices that purchasers must pay. The inventor believes that further improvements in engine/powertrain design and development and in engine control systems are unlikely to yield more than minimal fuel economy improvements.
Currently manufactured long haul commercial trucks commonly use large diesel engines in the range of 400-600 maximum horsepower as their prime movers. An engine having such a maximum power output is necessary to accommodate the peak power requirement for typical vocation drive cycles of those vehicles.
The current cost of hybrid powertrains does not justify their wide-spread adoption by the commercial trucking industry. Current sales of hybrid truck, buses, and coaches are predominantly in fulfillment of governmental contracts which use taxpayer funds as a subsidy for the additional costs of such “green” technologies in purchased vehicles.
Current large displacement fixed horsepower diesel engines operate within sub-optimal efficiencies, commonly within ranges between 800 and 2200 revolutions per minute (RPM). Because they accommodate changes in torque and power demand by varying engine RPM, such engines are inherently incapable of achieving optimum performance and best fuel economy.
Failure of a current diesel engine while a vehicle is on the road may create a hazardous condition for the driver and surrounding traffic and/or disable the vehicle to such an extent that unexpected delay, economic losses, and/or customer dissatisfaction become inevitable results of the failure.
Virtually all commercial trucks, buses and coaches on the roads today use conventional brake pads exclusively to decelerate the vehicle, converting the kinetic energy into wasteful heat. While such waste can be partially mitigated by a hybrid powertrain, hybrid powertrains are, as mentioned earlier, not currently cost-justifiable. A hybrid powertrain also inherently adds weight to a vehicle, a fact that adversely impacts fuel economy.